Metered dose inhalers and canisters for metered dose inhalers have been known for many years. It has also been known to provide canisters for metered dose inhalers in a range of sizes so that, for example, different numbers of doses can be dispensed from the differently sized canisters.
Developments in pharmaceutical formulations to be contained in metered dose inhaler canisters have lead to a demand for relatively smaller canisters. In part such demand has arisen from the provision of new pharmaceutical formulations which can require a smaller total volume of the formulation to be contained in the MDI canister. It has been appreciated that satisfactory results are not always attained simply by filling a standard sized MDI canister with a smaller volume of pharmaceutical formulation and that, to the contrary, it can be necessary for accurate dosing of the pharmaceutical formulation to match the size of the MDI canister to the required volume of the pharmaceutical formulation. WO02/056949 contains a useful discussion of the reasons for using smaller MDI canisters and the contents thereof are incorporated herein by reference, in particular page 2 lines 1 to 32.
WO02/056949 describes a shroud for a relatively smaller MDI canister which is provided in order to increase the effective external volume of the canister. The shroud can be in the form of a “cut down” conventional MDI canister into which the relatively smaller MDI canister is received. The shroud can be formed with an inwardly directed circumferential bead which limits the extent to which the relatively smaller MDI canister can penetrate into the shroud. In one version, the shroud can be secured to the relatively smaller canister only by an interference fit between a cylindrical inner wall of the shroud and a juxtaposed cylindrical outer wall of the relatively smaller MDI canister.
In another version as illustrated in FIG. 1, a complete relatively larger MDI can is used as the shroud. As shown in FIG. 1, the shroud 20 of this version of WO02/056949 can be in the form of an MDI canister of larger size than the canister 4 in which the aerosol formulation (i.e. the pharmaceutical formulation) is contained. The relatively smaller canister 4 can comprise a circular base 6 and a cylindrical sidewall 8 extending from the base to an open end 32. The open end 32 can comprise a circumferential flange 34 which is dimensioned to extend over the neck 21 of the relatively larger MDI canister (shroud) 20. The valve ferrule 18 can be crimped over neck 21, so trapping the circumferential flange 34 between the ferrule and the neck 21, and securing the relatively smaller MDI canister 4 within the shroud 20. A gasket seal 19 can be provided to form a seal with the circumferential flange 34.
Embodiments of the present invention seek to provide an MDI canister and a shroud which, in combination overcome, or at least mitigate, some disadvantages of the prior art. In embodiments of and variations of the invention such a combination can have an external profile which is similar to, and preferably substantially the same as, that of a conventional (relatively larger) MDI canister. In this way, modification of assembly machinery for the manufacture of the MDI is not required. Also, modification of the conventional housing into which an MDI fits for patient use can be obviated and patient expectations can be met. Patient compliance can also be enhanced.
Further, in embodiments of the invention different sizes of the relatively smaller MDI canister can be used in order to define internal volumes appropriate for different pharmaceutical formulations, while maintaining the same external profile of the combination.
Also, in embodiments of the invention secure mounting of the relatively smaller MDI canister within the shroud can be achieved, with little or no relative movement between the relatively smaller MDI canister and the shroud when so mounted. Such secure mounting can be achieved before attachment of the MDI valve to the combination and before filling of the combination with pharmaceutical formulation. Handling of the combined canister and shroud on a production line can thereby be facilitated.